The invention relates to a frequency detector for detecting the frequency of vibration of an apparatus.
Vibration sensing devices, which are economical and free from the problems which typically plague frequency-to-voltage converters, can find a wide variety of applications. For example, pavement ripping machines which are used to tear up concrete and asphalt prior to the roadway being resurfaced often rely upon chisels which are vibrated so that they repeatedly impact the road and, thereby, break up the old pavement. The frequency of vibration must be closely controlled, however, so that the chisels do not go into resonance which might tend to injure or destroy the machine. If a system utilizing a practical frequency sensing arrangement could be devised, then the frequency at which the chisels impact the road can be optimally controlled at just below the resonant frequency to yield the maximum effectiveness for ripping up the old pavement.
A second example where frequency-to-voltage detectors may be used is in the control of alternators. In vehicles such as those used for building and maintaining roadways, the engine of the machine drives a hydraulic pump which in turn drives a hydraulic motor for turning the alternator to produce the electric power utilized by the machine. It is desirable on such machines to precisely control the frequency of the output signal from the alternator. The vibration of the housing of the alternator is dependent upon the frequency of rotation of the rotor of the alternator and thus the frequency of the output signal from the stator of the alternator. A frequency detector for determining the frequency of vibration of the alternator housing can be used to control the pump for controlling the amount of fluid supplied to the hydraulic motor and thus the rotation of the rotor to precisely control the frequency of the output signal from the alternator.
Prior art frequency detection systems have been limited by temperature drift problems. Specifically, prior art frequency-to-voltage converters have relied upon capacitors to receive a cyclical input signal and to provide a steady state output signal whose value is dependent upon the frequency of the input signal. The output signal from such capacitors, however, is dependent upon the ambient temperature to which the capacitors are exposed. Thus, as the temperature drifts, the value of the capacitor will drift and provide an improper reading of the frequency of vibration of the apparatus being sensed.